Sensitive and selective detection of redox active substances, including those produced by pathogenic microorganisms, has important implications for both medical and environmental research, and in microbial fuel cells (Zhang et al., 2005, Curr Opin Microbiol 8, 276-281; Jacob et al., 2011, Current Opinion in Chem Biol 15, 149-155; Dietrich et al., 2008, Science 321, 1203-1206; and Ren et al., 2012, Microfluid Nanofluid 13, 353-381). A variety of amperometric and potentiometric techniques can be utilized to obtain information about the chemical composition of a solution (Pihel et al., 1995 Anal Chem, 67, 4514-4521; Buck et al., 2001, Anal Chem, 73, 88-97; Hengstenberg et al., 2001, Angew Chem Int Ed Engl, 40, 905-908; Muller et al., 1981, Neuro Meth, 1981, 4, 39-52), and may be used for development of the sensors for detecting redox active substances.
Electrochemical detection offers several advantages over other sensing schemes, such as fast analysis time, ease of use, and low limits of detection (Cheng et al., 2007, Electrophoresis 28, 1579-1586; Zou et al., 2008, IEEE Sens J 8, 527-535; Zevenbergen et al., 2007, Nano Lett 7, 384-388). Low-fabrication cost microscale electrochemical systems which have smaller sample volume requirements are attractive for the detection of molecules by this method. (Ino et al., 2011, Lab Chip 11, 385-388; Hwang et al., 2009, IEEE Sens J 9, 609-615).
Each of the amperometric and potentiometric techniques requires a stable reference electrode to provide accurate measurements. With the emergence of microfabrication techniques, miniaturized electrochemical sensors are now being developed and integrated inside fluidic systems (Lewis et al., 2010, Anal Chem, 82, 1659-1668; Kwakye et al., 2006 Biosens Bioelectron, 21, 2217-2223; Swensen, et al., 2009, J Am Chem Soc, 131, 4262-4266; Wang et al., 2008, Sensors, 8, 2043-2081; Straver, et al., 2012, Lab Chip, 12, 1548-1553).
Highly ordered graphite as well as hard and soft carbons are used extensively as the negative electrodes of commercial Lithium (Li) ion batteries. The high energy density values reported for these Li batteries are generally based on the performance of larger cells with capacities of up to several ampere-hours. One approach to overcome the size and energy density deficiencies in current two dimensional (2D) microbatteries is to develop three dimensional (3D) battery architectures based on specially designed arrays composed of high aspect ratio three dimensional (3D) electrode elements. For example, a micro 3D battery which has electrode arrays with a 50:1 aspect ratio (height/width), the expected capacity may be 3.5 times higher and the surface area 350 times higher than for a conventional 2D battery design.
Despite advancements in sensor technology, many challenges and significant need remains for the development of new systems and methods, particularly in the medical device and cancer diagnosis fields.